Exhaust-gas turbochargers are used for increasing the output of internal combustion engines. Turbochargers having a turbine wheel subjected to radial flow and an inner bearing arrangement of the shaft to which the turbine wheel is attached are mainly used in the low output range up to a few megawatts.
In uncooled exhaust-gas turbochargers, in which the gas-conducting passages are not cooled, the exhaust-gas temperature at the turbine inlet is higher, as a result of which the thermal efficiency of the machine and the output delivered to the air compressor per exhaust-gas quantity increase. The uncooled gas-inlet or turbine casing, which has a temperature of, for example, 650° C. during operation, is usually fastened directly to the bearing housing, which at 150° C., for example, is substantially cooler. In certain fields of application, the bearing housing, in contrast to the gas-conducting passages, is cooled to the aforesaid temperature. In addition, as described in EP 0 856 639, an intermediate wall serving as heat protection may be arranged in the region of an inflow passage leading to the turbine wheel, this intermediate wall shielding the bearing housing from the hot gas conducted in the inflow passage. In this case, the intermediate wall may be arranged such as to be separated from the bearing housing by an appropriate air or cooling-liquid zone and may have only a few, defined contact points in order to avoid as far as possible corresponding heat bridges to the bearing housing.
In conventional exhaust-gas turbines, straps or “profiled-clamp connections” or “V-band connections” are used in order to fasten the turbine casing to the bearing housing. In order to achieve as high an efficiency as possible, the air gap between the turbine blades and the turbine casing is to be kept as small as possible. However, this requires this casing wall and the turbine wheel to be centered relative to one another at all times, in particular during operation under full load and during corresponding thermal loading of all parts. Since the centering seat of the turbine casing relative to the bearing housing sometimes widens radially as a result of the large temperature difference between the bearing housing and the turbine casing, the turbine casing may become offset relative to the bearing housing and in particular relative to the turbine shaft mounted therein, i.e. the turbine casing is no longer centered in the radial direction relative to the shaft and the turbine wheel arranged thereon. Such an offset, which may be additionally encouraged by external actions of force, leads to contact between the turbine blade tips and the casing wall of the turbine casing, to corresponding abrasion or defects and, associated therewith, to considerable losses in efficiency of the exhaust-gas turbine. EP 0 118 051 shows how an offset of the hotter component can be avoided by means of groove/ridge connections arranged in a star shape and movable in the radial direction.
This conventional, but relatively costly, solution approach, in which the production process, in addition to pure turning operations, also includes milling operations, only permits a restricted number of different casing positions on account of the discrete number of groove/ridge connections. However, a solution approach in which the position of the turbine casing relative to the bearing housing can be set in an essentially infinitely variable manner is desirable.